Controlled moisturization of paper to eliminate curl

Abstract

A system which controls image dependent curl by moisturizing a sheet immediately after fusing, determines critical machine and environmental characteristics through a series of on-line sensors. An operator selectable table is used to indicate the type of sheet loaded in each sheet holding tray. Machine software then uses this information to determine how much moisture should be added to each side of the sheet in order to achieve a flat sheet when it reaches equilibrium

I claim: 
     
       1. A system that add moisture to copy sheets while en route in a copier/printer to curl, comprising: a pair of back-up rolls and a pair of cylindrical transfer rolls, each having an outer cylindrical surface, said transfer rolls and said back-up rolls defining a nip between said outer cylindrical surfaces;   a pair of metering rolls with one each of said pair of metering rolls in circumferential surface contact with one each of said cylindrical transfer rolls for wetting said outer surface of said pair of cylindrical transfer rolls;   a pair of servo motors with one each of said servo motors being connected to one each of said transfer rolls; and   a controller connected to said servo motors for controlling said servo motors in driving said pair of transfer rolls in a direction opposite to the direction of conveyance of the sheets at the nip area and thereby controlling the amount of fluid applied to each side of the sheets.   
     
     
       2. A system for controlled moisturization of copy sheets while en route in a copier/printer to eliminate curl, comprising: a pair of reservoirs with each of said pair of reservoirs storing a quantity of liquid;   a pair of back-up rolls, each having an outer cylindrical surface;   a pair of generally cylindrical transfer rolls, each having an outer cylindrical surface, said transfer rolls and said back-up rolls being aligned with respect to one another along their axes so as to define a nip between said outer cylindrical surfaces;   a pair of metering rolls with one each of said pair of metering rolls in circumferential surface contact with one of said cylindrical transfer rolls for wetting said outer surface of said pair of cylindrical transfer rolls;   a pair of servo motors with one each of said servo motors being connected to one each of said transfer rolls; and   a controller connected to said servo motors for controlling said servo motors in driving said transfer rolls in a direction opposite to the direction of conveyance of the sheets and thereby controlling the amount of fluid applied to each side of the sheets at the nip area.   
     
     
       3. A system for fixing a toner image to a copy sheet in an electrophotographic system so as to avoid the formation of a curl in the body of the sheet, comprising: first and second fusing rollers defining a nip therebetween, at least one of said fusing rollers being heated, wherein the fusing rollers serve to fix a toner image on a copy sheet through the application of heat and pressure to the copy sheet;   a sheet conditioning system for receiving a copy sheet from said fusing rollers, comprising; a pair of reservoirs with each of said pair of reservoirs storing a quantity of liquid;   a pair of back-up rolls with each having an outer cylindrical outer surface;   a pair of cylindrical transfer rolls, each having an outer cylindrical surface, said transfer rolls and said back-up rolls being aligned with respect to one another along their axes so as to define a nip when a sheet is present between said outer cylindrical surfaces;   a pair of metering rolls with one each of said pair of metering rolls in circumferential surface contact with one of said cylindrical transfer rolls for wetting said outer surface of said pair of cylindrical transfer rolls;   a pair of servo motors with one each of said servo motors being connected to one each of said transfer rolls for driving said transfer rolls; and   a controller connected to said servo motors for controlling said servo motors in driving said transfer rolls in a direction opposite to movement of the sheet at the nip area.     
     
     
       4. The system according to claim 3, including a tray for holding the copy sheets, and sensors for sensing relative humidity of said tray, room temperature and room relative humidity and transmitting signals indicative of the same to said controller. 
     
     
       5. A system according to claim 4, including inputs to said controller characterizing fuser roll temperature, dwell time, pressure roll temperature and moisturization fluid characteristics. 
     
     
       6. The system according to claim 5, including a lookup table that provides input to said controller of sheet characteristics encompassing sheet basis weight, sheet density, surface coating, thickness and percent of moisture change as a function of fuser temperature, and initial percent of moisture. 
     
     
       7. The system according to claim 6, wherein said controller either increases or decreases servo motor speed based on environmental inputs, machine characteristics, paper characteristics, and image type. 
     
     
       8. A method for replenishing the moisture that a copy sheet loses as it is heated in an electrophotographic machine of the type having a thermal fuser having a fuser roll and pressure roll, comprising the steps of: transporting liquid from a one each of a pair of reservoirs to one each of a pair of transfer rolls that are arranged so as to form nips with a pair of back-up rolls when a copy sheet is present;   transporting the copy sheet from the fuser through the nip of the rolls;   transferring liquid from the transfer rolls to one or both sides of the copy sheet; and   controlling the amount of liquid placed on said pair of transfer rolls in accordance with parameters including fuser roll temperature, pressure roll temperature, ambient relative humidity, percent of surfactant in the liquid, temperature of the liquid, side of the sheet imaged, and sheet characteristics including basis weight, sheet density, thickness, and sheet surface characteristics.